Date of Award

8-2014

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor

Carl P. Tripp

Second Committee Member

François G. Amar

Third Committee Member

Karl Bishop

Abstract

The mechanism of layer-by-layer (LBL) growth of a polyelectrolyte multilayer has remained controversial over two decades, partly due to the lack of a method that investigates the dynamics of the LBL process. In Chapter 2, attenuated total reflectance infrared (ATR-IR) spectroscopy was used to investigate the dynamics of LBL. Specifically, we used ATR-IR to study in situ the sequential adsorption of sodium polyacrylate (NaPA) and poly(diallydimethylammonium) chloride (PDADMAC) onto the TiO2 substrate. In addition to linear growth, we observed that NaPA, but not PDADMAC, layers show conformational rearrangement and diffusion into the growing PEM. Thus, we show that polymer diffusion is possible in the absence of exponential LBL growth. Furthermore, when the molecular weight of NaPA but not PDADMAC was doubled, we observed a linear PEM growth but no diffusion of NaPA layers. Thus, the ATR-IR method showed that linear growth occurs with or without polymer diffusion. The development of this method will help advance the knowledge of the molecular processes in LBL growth and provide data for the validation of existing models.

In Chapter 3, we investigate the control of LBL growth by using an electric field (E-Field) which controls the diffusion of polymers into and out of the PEM film. Using an ATR-IR setup, we demonstrate two patterns of PEM growth in which there is non-linear increase or decrease. Thus, our combined E-Field and ATR-IR methods offer two more ways to control LBL without changing any chemical parameters of the polymers or solutions.

In Chapter 4, we investigate the effect of polymer packing density and the active site density on analyte capture efficiency. In particular, we self-assembled block copolymers on a membrane and reacted the copolymers with a siderophore. It is demonstrated that at higher packing densities of the polymers, there is a flow rate dependence in the Fe3+ capture efficiency of the siderophore. Moreover, we developed a molecular imprinting (MI) method in which siderophores were bound with Fe3+ before anchoring them onto the polymer. The method included a step in which the MI Fe3+ could be removed from the active sites, making them available for reuse. The MI approach circumvented the flow rate dependence in capture rate. It also provided the platform to obtain optimum packing density of the binding ligands and hence, optimum efficiency of the sensor.

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